Preheat oven to 180°C/350°F. Line a large baking tray with greaseproof paper.
Melt the butter in a small saucepan. Set aside to cool for a few minutes whilst you prepare the rest of the ingredients.
10 tablespoons unsalted butter
In a medium mixing bowl, combine the all-purpose (plain) flour, cornstarch (cornflour), baking powder, baking soda (bicarbonate of soda) and fine sea salt. Stir together using a whisk, to ensure all the ingredients are evenly distributed.
2 ½ cups all-purpose (plain) flour, 2 teaspoons cornstarch (cornflour), 1 teaspoon baking powder, ½ teaspoon baking soda (bicarbonate of soda), ¼ teaspoon fine sea salt
In the bowl of a stand mixer, combine the brown sugars and granulated sugar with the slightly cooled melted butter. Mix on medium speed, until well combined. (Alternatively use a large mixing bowl and an electric hand mixer).
¼ cup packed light brown sugar, ½ cup packed dark brown sugar, ¼ cup granulated sugar
Add the egg and the vanilla to the butter and sugar mixture and continue to mix on medium speed until well combined.
1 large egg, 1 teaspoon vanilla extract
Add the flour mixture and mix on low speed until no streaks of flour remain.
Add the chocolate chunks and the popcorn (remember to check for any unpopped kernels in the bag first!) to the cookie dough. Mix on low speed until evenly distributed throughout the dough.
7 ounces dark chocolate, 4 cups popcorn
Roll into approximately 2 tablespoon-sized balls (you should get 24 cookies from this mixture) and place on the prepared baking tray. You should get 6-8 on a tray at a time.
Bake in the preheated oven for 8-10 minutes (mine took 8 minutes in a fan-assisted oven) until lightly golden at the edges. They should still feel soft and underbaked in the centre – that’s what you want! They’ll continue to bake as they cool.
Sprinkle the tops with flaky sea salt and leave to cool on the tray (or for as long as you can bear to wait!) Enjoy!
flaky sea salt, to finish